I am a 2nd year medicine resident from MGH spending one month in Dhaka, Bangladesh to work in an immunology lab studying responses to cholera. I received a Center for Global Health Travel grant to pursue this work, and in these blogs will introduce the topic of cholera with a few details about the research I am doing and the institution where this research is conducted.
In Bangladesh, the most densely populated country in the world, the capitol city of Dhaka contains at least 15 million residents, many of whom live in urban slums. Dhaka is a colorful and chaotic city, and every day thousands of people come to Dhaka from the countryside of Bangladesh in search of a better life. Nearly all cholera patients come from the urban slums, particularly one called Mirpur. This slum contains around 3 million people living in shacks and makeshift residences, and the water supply is heavily manipulated by people tapping in water lines illegally. This manipulation leads to sewage lines mixing with the water supply. Most people do not boil or treat their water prior to using it, since fuel for a fire and water treatment supplies cost money. In Dhaka, diarrhea is a common and somewhat normalized fact of life for both visitors and the Bengali people, especially children. The usual causes are E coli spp as well as rotavirus, shigella, typhoid and other bacterial, fungal and viral causes, in addition to cholera.
Cholera occurs in areas of the world where the 20th century innovations of clean water and latrine use are not yet realized. There are 3-5 million cases of cholera each year and most cases are in southeast Asia. Children are disproportionately affected. The organism that causes cholera, Vibrio cholerae, lives in the environment in the Ganges Delta, which is the largest river delta in the world. This flat, easily flooded plain includes much of Bengal in northeastern India, as well as Bangladesh. This area has supported large populations for thousands of years, and for centuries cholera has caused disease both year round and in epidemic spikes during the two rainy seasons each year. V. cholerae is spread by fecal-oral transmission and causes a range of disease from asymptomatic or subclinical infection to severe dehydrating diarrhea that can cause death within 6-12 hours if untreated. In this short time, patients can lose more than 10% of their body weight in fluid losses, and adults can loose 20 liters or more. The primary treatment is rehydration, and in most patients oral rehydration is sufficient. In cases accompanied by severe vomiting, or dehydration that progresses to depressed consciousness, intravenous rehydration is required. Antibiotic treatment decreases the severity of disease and shortens the duration of symptoms. In Dhaka, tens of thousands of cases of cholera occur each year.
There are several vaccines for cholera, and these have improved significantly in the last several years. They provide partial protection for several years, but are not very effective in children. My work in immunology is focused on understanding the immune response to natural cholera infection, in an effort to understand what creates the longer-lasting immunity we see after natural infection versus the partial, shorter-lasting protection observed after vaccination.